# include <iostream>

using namespace std;
void test01(){
    string s1;
    cout<<"str1="<<s1<<endl;
    const char*str="hello world";
    string s2(str);
    cout<<"str2="<<s2<<endl;
    string s3(s2);
    cout<<"str3="<<s3<<endl;
    string s4(100,'s');
    cout<<"str3="<<s4<<endl;
}
int main() {
test01();
    return 0;
}
